Field mapping

06

New “survey grade” GPS equipment

For many of our mapping projects and contracts, from mapping storm sewers to electrical networks, we’ve needed more accuracy than our “resource grade” Trimble GPS units can provide. This has been particularly true for our UAV imagery. Since we’re producing images with resolution of between 1-5 cm, we need ground control that’s as accurate or better than this resolution. Our Trimble units under ideal conditions can provide 15-30 cm horizontal accuracy — not good enough. Plus, we’re hearing more about local government units purchasing higher-accuracy devices which our students need exposure to.

So, after looking around at the range of options, we purchased a X90-OPUS GPS from iGage in Salt Lake City. This is a “static” GPS device meaning that we set it up over a location — let’s say a UAV ground control point — and let it collect GPS satellite information for at least 15 minutes. So, we can’t stick the device on our UAV and fly it around. With 15 minutes of data per point, we should get around 1 cm horizontal accuracy and can increase this accuracy with longer occupation times.

For solutions, the system uses the National Geodetic Survey’s free OPUS service which does all the advanced calculations with our field data and corrections from a network of GPS receives across the country, the CORS network. The system also has a map of expected accuracy for various occupations times. Unfortunately, we’re close to a hole (south of us) in the CORS network that will hopefully be filled soon.

What’s amazing to me is the cost of this system — around $2,100 for the GPS unit plus the range pole and tripod needed for field deployment. Survey-grade GPS used to run $15-20k just a few years ago — our resource-grade Trimble’s were around $6,000 a piece.

Looking forward to getting out with the students to figure out our new device.